The use of small compact electric motors inside, or in close proximity to, an aircraft wheel, for direct drive, presents a problem relating to the provision of the required amounts of torque. Generally, for moving an aircraft from rest, the torque required is extremely high, so that the torque versus speed characteristics of the load, and the maximum speed characteristics of the load when driven, fall well outside the ideal predicted by motor scaling laws. This means that a motor sized to produce the torque necessary for direct drive of the load will be operating at well below maximum speed, and thus well below maximum power levels. The active materials of the machine will be underutilized, the machine will be far heavier than necessary, and the machine efficiency will be poor.
Gearing can provide a higher speed, lower torque motor with a higher torque option to enable a motor to be housed within a wheel. The wheel itself is expected to operate during takeoff and landing at much higher than normal motoring speeds. This presents a significant problem, because, in these cases, the wheels may be rotating faster than the motor and may accelerate the motor via the gearing system. Under these conditions, the motor would be forced to spin at much higher speeds than rated.
U.S. Pat. No. 3,711,043 to Cameron-Johnson discloses an aircraft drive wheel having a fluid-pressure-operated motor housed within the wheel and two planetary gear stages housed in a gear box outboard of the motor, the final drive being transmitted from a ring gear of the second gear stage, which is inboard of the first stage, to the wheel through an output drive quill coupled, through a disc-type clutch if desired, to a flanged final drive member bolted to the wheel.
U.S. Pat. No. 3,977,631 to Jenny discloses a wheel drive motor selectively coupled to an aircraft wheel through a rotatably mounted aircraft brake assembly in order to drive the wheels of an aircraft. The normally non-rotating stator portion of a conventional aircraft brake assembly is rotatably mounted about the wheel axle and is rotatably driven through a planetary gear system by the wheel drive motor.
A solution disclosed in PCT application WO2005/035358 discloses a mesh connected high phase order induction motor, situated in close proximity to, and preferably within, the nosegear. The mesh connection enables variable inductance so that the machine has a range of speed/torque profiles available.
Various guidance systems for aircraft taxi are disclosed in the art. The degree of automation in taxiing may vary.
U.S. Pat. No. 6,411,890 to Zimmerman discloses a method for the guidance of aircraft on the taxiways of the airport apron with position lights located on the taxiways and, possibly, other locations on the apron. It comprises the following components: a navigation system to determine the current aircraft position; a sensor on the aircraft to detect position and measure lights, reference information including light positions, a comparison of the path pursued by the navigation system with the reference information, and using the detected lights as waypoints for the navigation system. The method determines the current aircraft position more precisely than purely through the navigation system, and generates guidance information based on the determined aircraft position. The invention further discloses an additional sensor for the detection of lights and their position measurement. The latter should be performed with a precision of approx. 10 cm. Video cameras and scanners, for example which can be advantageously arranged on the aircraft main landing gear, are suited for this task.
U.S. Pat. No. 6,690,295 to De Boer teaches a device for determining the position of an aircraft at an airport, including sensors for detecting radio signals originating from a vehicle. The sensors are positioned at regular intervals from one another on parts of the airport which are accessible to the vehicle. The sensors are fitted in light positions of runway lighting provided at the airport on taxiways, take-off and landing runways and on platforms. The signal originating from a radio altimeter of an aircraft is used as the radio signal. Data communication takes place from the sensors via power supply lines of the light points. A central processing device is provided with warning means to generate a warning if the detected position of the vehicle is outside a predefined area at the airport which is permitted to the vehicle.
A sophisticated control system is utilized in a Space Shuttle Orbiter vehicle. The vehicle uses a conventional type of landing system having an aircraft tricycle configuration consisting of a nose landing gear and a left and right main landing gear. The nose landing gear is located in the lower forward fuselage, and the main landing gear is located in the lower left and right wing area adjacent to the mid-fuselage. The nose wheel is equipped with a ground proximity sensor, in order to determine Weight on Nosegear (WONG), a parameter required during landing. After landing, when WONG and other safety parameters have been established, Nose Wheel Steering (NWS) is enabled. One or more steering position transducers on the nose wheel strut transmit nose wheel steering position feedback to a comparison network so that the nose wheel commanded and actual positions may be compared for position error.
Braking is accomplished by a sophisticated system that uses electrohydraulic disk brakes with an anti-skid system. Only the two main gear sets have braking capability, and each can be operated separately. Two primary steering options are available. By applying variable pressure to the brakes, the crew can steer the vehicle by a method called differential braking. Also, by selecting nose wheel steering, the crew can use the rudder pedal assembly to operate an hydraulic steering actuator incorporated in the nose landing gear. The crew can also use the rudder to assist steering while at higher ground speeds.
Each main landing gear wheel has two speed sensors that supply wheel rotational velocity information to the skid control circuits in the brake/skid control boxes. The velocity of each wheel is continuously compared to the average wheel velocity of all four wheels. Whenever the wheel velocity of one wheel is a predetermined percentage below the average velocity of the four wheels, skid control removes brake pressure from the slow wheel until the velocity of that wheel increases to an acceptable range.